WORKSHOP NOTES Invited Experts:

James Belke, EPA Don Ermak, LLNL

Martin Goodrich, Baker Risk (absent due to family emergency) Greg Jackson, U. of Maryland

Tom Spicer, U. of Arkansas Doug Walton, NIST

Kin Wong, DOT Agenda

WEDNESDAY, FEB. 23

2.PM INTRODUCTORY REMARKS Miller, Belke

---2:15 PM VAPOR CLOUD Lehr

---THURSDAY FEB 24

8:30 AM FLARE Simecek-Beatty

---10 AM POOL FIRE Lehr

---11 AM BLEVE Lehr

---1 PM USER INTERFACE Muhasky

---2:30 PM PANEL DISCUSSIONS All

---3:30 PM EXPERT PRESENTATIONS Walton

Vapor Cloud Notes

Efficiency factor: Currently, the model uses 5 % of the cloud mass for calculating explosive energy if the incident is designated as an accident and 20% if it is deliberate.

Alternative suggestions were to take the actual fraction of gas between the UFL and LFL or take the mass fraction that is above 0.9 LFL. Recommended that BakerRisk comment on appropriate efficiency factor.

Fireball LOC: Current footprint follows Risk Management Program (RMP) guidance by matching fireball hazard to LFL. Several felt that this was not conservative enough.

Suggestions included using 0.9 or 0.6 LFL or calculating actual radiation hazard. Pointed out that fireball could be secondary effect from vapor cloud explosion.

Overpressure: Model currently transforms cloud into semi-ellipsoid shape, uses

expanding piston approach and Strehlow method to calculate overpressure. Baker-Strehlow was considered an acceptable approach although multi-energy was mentioned as an alternative. The turbulent flame speeds are now calculated based on fuel reactivity and obstacle density utilizing the tables in Woodward's book. However, none of the Mach numbers exceeds 1, implying no detonation case. It was suggested using the highest Mach number curve in the Baker-Strehlow graphs, assuming that there was a hard ignition source strong enough to start detonation. If this were done, then questions of reactivity and obstacle density would not have to be asked. Consideration was also given to new table values sent by BakerRisk.

There was a lot of discussion of impulse versus overpressure. Impact from the overpressure wave is a function of both. Problem is similar to mapping concentration

versus dosage for chemical inhalation. Also there was some discussion on setting ignition location. Center of cloud seemed to be conservative consensus.

Flare notes

View factor : There was discussion about using a cylindrical optically dense flame, as in the pool fire model rather than using point source view factor. One recommendation was to always assume a clear, dry day. This is equivalent to neglecting atmospheric

dampening.

gas exist velocity: Model currently assumes that flame will blow out when Mach number exceeds 0.5. Suggested that there may be a better number or that this restriction be dropped (flame could simply start farther away from source). Match rate of combustion to release rate to achieve steady state case. Most felt that horizontal jets also be allowed rather than only vertical ones. Model will not work well with oil fires due to smoke generation.

2-phase: Model currently transforms 2-phase release into gas release. Some pointed out that 2-phase incident could produce both flare and pool fire. Suggested reviewing existing references on 2-phase flow to see how to handle for flare situation BLEVE

fireball size: Experts agreed that limits should be placed upon fireball size. One

suggestion is to limit fireball mass to three times the fraction that is adiabatically flashed.

Another is to restrict user input to largest common propane tank. Compare our simplified model to results from more sophisticated models.

terminology: Consensus was that careful wordsmithing needs to be done to maintain consistency of language, technical accuracy, and fit within common usage.

other hazards: Model only considers thermal hazard. People agreed that user should be warned about all hazards, including overpressure and shrapnel. Some discussion on shrapnel models

Pool fire

pool size: Model currently stops spreading when the burn rate equals the chemical release rate. Recommendation was to eliminate this restriction and stop spreading only when minimum thickness was reached. Need to ascertain upper limit on model applicability for large fires.

pool shape: Suggested that LOC footprint be circular rather than elliptical in order to be more conservative.

burn regression rate: Approximation of burn regression rate as ratio of heat of combustion to heat of vaporization may not be good approximation, particularly for

cryogenic spills. Model should estimate fires of diesel and gasoline as well as existing ALOHA flammables.

User interface

mixed risk: There was considerable discussion but no consensus on the best way to handle display of competing hazards. Some thought user should simply see worst risk while others favored displaying all risks.

User guidance: There was considerable discussion but no consensus on the best way to interact with the user; whether to have the user trek through a specific scenario or use check boxes to look at simultaneous scenarios.

USABILITY TESTS (performed by Mary Evans)

Table 1, below, lists usability-related observations made last week during the International Oil Spill Conference, along with related design inferences.

How observations were made:

These observations were made during five usability tests of the new version of ALOHA incorporating fires and explosions modeling. During each test, a Coast Guard member experienced in hazmat response served as the test participant. I observed each participant as he or she used ALOHA to respond to a hypothetical scenario involving a release from a benzene tank, propane cylinder, or natural gas pipeline. Following the test, each participant was asked a series of questions to elicit his or her understanding of fires and explosions-related terminology, interface features, and output plots in ALOHA.

Summary of findings:

Overall, the new version of ALOHA was enthusiastically received (“Wow!,” “I like this!” “I think this is really good”), and test participants remarked that the new functionality will be useful for them. However, they generally found it difficult to understand some of the new terminology related to fires and explosions modeling and to interpret output plots. While using the model for fires and explosions modeling, they felt unsure at points where they had to make choices between available alternatives. They recommend that explanations, legends, and help texts be added to the model to boost their understanding of key concepts, use of the model, and the model’s output. The tests also uncovered pre-existing usability problems, which are listed in Table 1.

Table 1. ALOHA usability findings.

Observation Design inference

Participants don’t understand the term “overpressure.”

(“Are we talking BLEVE?””Some firefighters will know this is a BLEVE.” “I guess it’s over, beyond where explosion could happen--??” “I’m guessing that’s the

ADDRESS IN HELP, USING TERMS FAMILIAR TO RESPONDERS. COULD THIS CHOICE BE REWORDED TO

(“Are we talking BLEVE?””Some firefighters will know this is a BLEVE.” “I guess it’s over, beyond where explosion could happen--??” “I’m guessing that’s the level of gas pressure inside the explosive plume.”

“Wait,..it’s telling me where the damage is from the pressure wave itself, not the fire. I just had to think through it.”)

TERMS FAMILIAR TO RESPONDERS. COULD THIS CHOICE BE REWORDED TO SOMETHING LIKE “VAPOR CLOUD EXPLOSION

(FOOTPRINT WILL SHOW AREA OF IMPACT FROM OVERPRESSURE WAVE)”?

Participants don’t understand the term “vapor cloud flash fire.” (“…the fireman doesn’t know what this means.”

“So this is more like flash point, and this is more like fire point?” “I don’t know why I should be concerned about this”)

Revise language, use just-in-time documentation, and address in help, using terms familiar to responders.

Could this choice be reworded to something like

“Vapor cloud flash fire (footprint will show area affected by heat from the burning cloud)”?

Most participants could not identify the release point on an overpressure plot, when asked. (“The railcar could be anywhere here. The ground zero is where the ignition happens within the cloud.” “Can’t tell—the wind is from the east, but…This is kind of confusing. It would be helpful if it was marked….” “Looks like the release point would be at the center of the circle.” “Where’s the center…Where’s the cylinder on this? I’d want to know where’s the leak? Where’s this supposed to be? I know I’m supposed to look at this and tell…I need to know where I need to evacuate…” “At the 0, 0, I assume, though it seems to be a little off center. It really doesn’t say.”)

Label the release point.

Consider drawing wind direction arrow on plot.

MOST PARTICIPANTS DON’T UNDERSTAND THE

DISTINCTION BETWEEN HARD AND SOFT IGNITION. (“I HAVEN’T HEARD OF THAT BEFORE.” “I’M GUESSING SOFT IGNITION.” “I WOULD CLICK HELP TO FIND OUT ABOUT THIS CHOICE” “I DIDN’T NECESSARILY KNOW WHAT THEY MEANT, BUT WITH THE BLURBS AFTER THEM IT WAS PRETTY CLEAR. MY FIRST THOUGHT IS IF THESE TWO SHIPS HIT WOULD THAT QUALIFY AS A HARD IGNITION.”) AND ADDRESS FURTHER IN HELP.

Participants noted that “Obstacle congestion” could be interpreted differently in different places and

circumstances. Also, the same location—the area around the convention center—was evaluated differently by different participants, who chose either medium or high.

(“What that means to someone in a city may be different from someone in a small town. NYC would be 100%

congestion all the time. Coming from a city, I’m sure it’s medium or high.” “If we have a chemical that’s heavier than air, an obstacle can be a foot high.” “I guess it’s what’s around the area: Are there a lot of trees and buildings to impede movement of cloud?” “I’d infer that means the number of objects in the vicinity of the

explosion.” “This is pretty qualitative. What is 10-40%?

Here, I’d go medium because there’s no tall buildings.

From a maritime perspective, I’d probably choose low.”

“…the deck of a ship is pretty low. At most it’s probably medium, but low is probably going to give me the worst case so I’ll choose it.” “That one, I would really need the help screen. Would it be single-storied buildings or normal ground? How does it apply to a ship? To a container ship, stacked high, vs. a tanker? I’d want to go worse-case scenario, to CYA. Maybe have the worst case choice be the default.”)

Address in help and in just-in-time documentation (e.g., list some real-life examples in parentheses following each choice). Consider adding subcategories (e.g., urban/rural).

The term “high power explosive device” is not clear to participants. (“…high power explosive device—TNT?

What are we talking about here? This explosion is going to ignite another explosion?” “What’s a high power explosive device: a grenade or an atom bomb?”)

DEFINE THIS TERM IN HELP, OR REWORD IN INTERFACE. CONSIDER JUST-IN-TIME

DOCUMENTATION.

Participants appear to think in percentages rather than fractions. (“0.6 LEL. I assume that’s 60% of the LEL.”)

Reword as “60% LEL”

Participant would like to see both LEL and UEL as LOCs under the downwind dispersion option. (“I teach that you shelter in place for toxic hazards, evacuate for flammable hazards…Knowing LEL is important, knowing if you’re above UEL is also important, because you have to go through the flammable range to go back to where you’re safe.”)

Consider including LEL as LOC along with fractions commonly used by

responders, especially 10%

LEL. Consider including UEL as an LOC choice for the downwind dispersion option.

Most participants select Computational when completing a scenario, though it’s generally not a needed step for their work, and leaves them confused.

Consider moving this option to an Options submenu.

Four of five participants setting up a scenario have difficulty recognizing what to do next after entering location, chemical, weather, and source strength. They mouse around in menus and select other options

(Computational, Source Strength, Conc & Dose) before eventually selecting Footprint. (“Now I think I’ve filled out everything it needs..I’m looking for a button…”)

Generally arrange menus so the items one must select to complete a model run are in proper sequence and other things are out of the way.

Consider moving Footprint to top of Display menu and moving other items in this menu to a single Display Options dialog.

When source strength is too low for a footprint to be generated, the resulting message disorients participants.

They appear to take it as an error message.

Revise message wording to make the distance estimate more prominent.

Participant 2, trying to model vapor cloud ignited by lightening, can’t tell which Footprint option to choose (downwind dispersion, overpressure, or flash fire). (“This is that area where it would be dispersed to, but how the lightening would affect that…I don’t see how to find that.”) Others have difficulty making this choice as well (“Now, this isn’t intuitive…”)

Use just-in-time documentation, with

examples if space allows, to explain the three choices.

Relate choices to real-life circumstances responders could encounter. Consider including a decision key to help users choose between explosion and flash fire.

Some participants understand the default LOCs for overpressure, but additional explanation would help others. (“I’d figure it would show you footprint, with red area where 50% would die.” “It’s in units of PSI so it’s obviously some pressure issue, but it’s related to

fatalities…so I’m not understanding what this is about. It must mean that this pressure [points to red LOC] would relate to half the people being killed.”) One participant expected to see inhalation LOCs along with overpressure LOCs (“This seems like it would be the sound of it---eardrum rupture—but would it just hurt your ears? What about respiratory hazards?”)

Include interpretation guidance in Help. Explain that users should select Downwind dispersion option to assess respiratory hazards.

Participants don’t understand the wind direction

confidence lines on flash fire footprint (“The dashed line could be the high flammability limit—this would just be a guess.” “I’m wondering if this is the LEL…I’m not sure how to interpret those…” “I’m assuming that the dashed line would be the extent of the flash…no it must be limited to the inner zone…so I don’t know what the dashed line indicates. It should go in the legend.” “Just the dispersion area of the propane? I don’t know. It should go in the legend.” “I assume that would be possible wind shifts, but I’m not sure and there’s no key.”)

INCLUDE LEGEND WITH DEFINITION ON PLOTS.

Participant 4 (a toxicologist) really likes ALOHA’s error messages (he had typed “mph” into the wind direction box). (“Nice error handler!!”)

Continue including error messages in same format.

Two participants left “Gas in tank” as the default for a liquefied gas scenario; one was able to recover only when prompted. Both backed up repeatedly, trying different options, until they finally chose to model a liquid in a tank.

Consider just-in-time documentation. Reconsider the existing default for gases that are usually liquefied in containers. Is it possible to change the default to liquid for those chemicals that are normally stored liquefied above their boiling point?

Participants occasionally access ALOHA’s Helps by clicking interface buttons.

Help buttons right next to items of concern appears to be an effective way to provide Help (in contrast to CAMEO’s single-entry Help, which no one used).

Participant was confused by 1-hour cutoff on source graph (“Maybe I don’t understand something, but I’d expect the pressure to decline over time, not a sudden cutoff like this.”)

Add explanatory note to graph.

Participant did not know what lines represent on

Concentration graph (“I need a legend to tell me what this blue line and this red line is”)

Add legend to

Concentration graph for indoor and outdoor lines.

Participant did not understand area of flash fire (“I’m assuming that’s the area that would be engulfed by flame in an explosion.”)

RECONSIDER

TERMINOLOGY, USE JUST-IN-TIME DOCUMENTATION.

Participant recommends including reference for .6 LFL use along with help. (“ALOHA uses .6 LFL, but why? A link to a help would be good here.”)

In the Help for this dialog box, describe reference for the .6 LFL choice and include interpretation help.

Explain why it’s .6 and not the 10% LEL value

commonly used by responders. Consider showing 10% LEL isopleth on the plot, since it seems to be commonly used to find the isolation distance.

Participants would like an indication of wind direction and release timeframe (duration) on plots. (“This scenario doesn’t include a timeframe…a wind direction arrow or timeframe: a scrollbar to let me scroll the time out and back.” “Time should show up on the plot.”)

ADD WIND DIRECTION

Participants don’t know how to make decisions about time of ignition, and make choices in a variety of ways. (“I keyed on ‘after the beginning of the release’ and assumed

‘what if it happened right now? We’re 15 minutes into the release.’” “do I have to put a number here?…I’ll put 10 minutes…”)

Consider participant’s suggestion to include an ignition time slidebar on the plot window.

Participant commented that ALOHA interface is more cumbersome to work with than other interfaces he’s encountered. (“One thing about ALOHA is that you have to go back through all the screens to change something.

Other interfaces, you can click tabs, and quickly adjust a tank dimension, for example.”)

IN NEXT MAJOR UPGRADE, CONSIDER REVISING INTERFACE TO BE MORE LIKE ADIOS II (IN WHICH IT’S POSSIBLE TO ADJUST INDIVIDUAL INPUTS FROM THE MAIN PROGRAM WINDOW).

Plots using red, orange, and yellow zones are

well-received (“I like this—red, orange, yellow footprints make sense intuitively. This is the kind of thing I want to see graphically.”)

Maintain color scheme, as well as existing pattern scheme supporting color-blind users.

Participants would like to see detailed, complete legends and helps, and titles on plots (“…having a help screen here, definitely, understanding what psi is, what 50%

fatalities means…From the responder perspective, define down to Nth degree.” “There should be a title on the graph, with everything labeled. So you could hand it off to a decision-maker.” “This product has to explain

everything to the layman.” “…the legend isn’t

ADD DETAIL TO EXISTING LEGENDS; ADD TITLES WHERE MISSING; PREPARE DETAILED HELPS GEARED FOR A RESPONDER

AUDIENCE.

graph telling me?” “So is this hazardous? Am I going to drop dead? Is this on fire? What does this mean?”) ALOHA printouts need timestamps. (“There’s no date and time on this, so no one knows when this is. Later, another gets printed out, they get mixed together, no one knows which is current. The person who made it may not be in the room.”)

ADD TIMESTAMPS TO ALL PRINT OUTPUT.

LEL is more meaningful to responders than LFL,

according to one participant. (“Most responders operate in the world of LEL. Might want to define LFL.”)

Research to find out

whether LEL is indeed more commonly used. Consider using LEL in place of LFL.

For puddle cases, participant would like to see ground type choices for marine situations, especially steel deck (he chose Concrete, reasoning that it would not soak up product like the other ground types). (“In ALOHA, when it says choose your surface, a lot of times we’re going to use this on a ship. It seems more based towards ground and land based properties. On decks, the sun’s going to send heat. There’s a problem with latent heat. A lot of decks

For puddle cases, participant would like to see ground type choices for marine situations, especially steel deck (he chose Concrete, reasoning that it would not soak up product like the other ground types). (“In ALOHA, when it says choose your surface, a lot of times we’re going to use this on a ship. It seems more based towards ground and land based properties. On decks, the sun’s going to send heat. There’s a problem with latent heat. A lot of decks

In document Technical documentation and software quality assurance for project Eagle-ALOHA (Page 41-51)